Answer: The Bubonic Plague

Sometimes the best thing for a brilliant scientist is a little time alone, and time alone is exactly what an outbreak of the bubonic plague granted Isaac Newton in 1665. The outbreak of the plague, known as The Great Plague, was the last major outbreak in England and was serious enough to kill over 15% of the citizens of London.

The threat of the plague led Cambridge University to close its doors during the outbreak, which in turn sent Newton home for almost two years. During that extended sabbatical in his home study, Newton laid down the groundwork for infinitesimal calculus (as well as the foundations of his theories on planetary motion, light, and color).